Electrosurgery typically utilizes the application of high frequency currents to cut or ablate tissue structures, either utilizing a monopolar or bipolar configuration. Monopolar configurations utilize an instrument having a single electrode and rely on externally connected return electrode placed on the patient whereas bipolar configurations utilize both an active and return electrode on the instrument itself for application of a current between the electrodes.
Electrosurgical procedures and techniques are particularly useful in reducing patient bleeding and trauma typically associated with surgical procedures. However, the radio frequency (RF) currents typically used by electrosurgical instruments during procedures can sometimes induce involuntary and undesired stimulation in nearby neuromuscular structures causing discomfort to the patient as well as compromising the safety of the patient. Attempts to avoid such undesired stimulation have included increasing the operating frequency of the electrosurgical generator to mitigate the stimulating effects of the current. Other attempts have included reducing the rate of change of the output voltage or reducing the overall magnitude of the RF voltage and current.
Increasing the operating frequency may increase the costs associated with the power supply as well as compromise the performance of the electrosurgical instrument. Moreover, an increase in operating frequency may also increase the magnitude of undesired RF leakage currents. Likewise, limiting the rate of change of the output voltage or reducing the magnitude could also degrade instrument performance because such a limitation or reduction may limit the response time of the electrosurgical system or limit the total power delivered to the target tissue.
Mitigating or eliminating undesired electrical stimulation in surrounding structures may be particularly useful in procedures where electrosurgical instruments are used in electrically conductive environments, particularly regions which may be filled with blood, irrigated with saline, or the like. In these types of operating environments, such instruments may be utilized to cut and/or ablate tissue, such as articular cartilage, meniscal tissue, etc.
Accordingly, there is a need for electrosurgical instruments which can deliver sufficient power to targeted tissue while reducing the magnitude of RF current delivered not only to the tissue but also to surrounding structures so as to mitigate or eliminate undesired stimulation.